import java.lang.Math;
import java.util.Scanner;

public class Test12 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();

        try {
            showArea(a, b, c);
        }catch (Exception e) {
            System.out.println("异常 " + e);
        }
        finally {
            System.out.println("end");
        }
    }

    static void showArea(int a, int b, int c) throws NewException{
        double p = (a + b + c) / 2.0;
        double ret = p * (p - a) * (p - b) * (p - c);
        if (ret <= 0) {
            throw new NewException();
        }

        double s = Math.sqrt(ret);

        System.out.println(s);
    }
}

class NewException extends Exception {
    public NewException() {
        super("无法构成三角形");
    }
}